Switching mode power converter is a type of commonly used voltage converter circuit which is generally configured to provide load with regulated output voltage or current (i.e., load voltage or load current) based on unregulated supply voltage.
FIG. 1 shows a circuit diagram of a prior art boost converter circuit 10. The converter circuit 10 comprises: a first inductor L1, a first transistor M1, a second transistor M2, and an output capacitor CO. The first inductor L1 is coupled between an input terminal IN and a switching terminal SW; the first transistor M1 is coupled between the switching terminal SW and a ground terminal GND; the second transistor M2 is coupled between the switching terminal SW and an output terminal OUT; and the output capacitor CO is coupled between the output terminal OUT and the ground terminal GND. The second transistor M2 can be a P-type channel metal oxide semiconductor field effect transistor (“PMOS”). When the converter 10 is disabled, voltage at the input terminal voltage (i.e. an input voltage VIN) and voltage at the switching terminal (i.e. a switching voltage VSW) are higher than voltage at the output terminal (i.e. an output voltage VOUT), and a body of the second transistor M2 should be coupled to the switching terminal SW to prevent the body diode D1 from being turned ON. When the converter circuit 10 is enabled and the first transistor M1 is turned ON, the switching voltage VSW is close to zero and substantially lower than the output voltage VOUT. In this circumstance, the body of the second transistor M2 should be coupled to the output terminal OUT of converter circuit 10 to prevent the body diode D2 from being turned ON. Therefore, a body selection circuit 101 is needed in converter circuit 10 to selectively couple the body of the second transistor M2 to a high electric potential terminal of converter circuit 10 in different conditions. Usually, such a body selection circuit 101 has very complex circuit configuration and control logic, which is hard to design, prone to design mistakes and resulting in large layout size. Moreover, the cost performance of technical proposals adopting body selection circuit is especially low when the load current of the converter circuit 10 is relatively small (i.e., an on-resistance of the transistor M2 can be relatively high with a small layout area). As a result, design of more optimized circuit structure to avoid using a body selection circuit in boost converter circuit is a challenge faced by persons skilled in the art. In addition, the boost converter circuit 10 as shown in FIG. 1 can only provide an output voltage VOUT higher than the input voltage VIN. Optimizing the circuit so that it can also provide an output voltage VOUT lower than the input voltage VIN is another challenge faced by persons skilled in the art.